1. Field of the Invention
The present invention relates to a gate for vehicles having a radar apparatus used for preventing a collision between vehicles.
This application is based on Patent Application No. Hei 11-6263 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
As a constituent of a collision or clash preventing system mounted in a vehicle, a radar apparatus has been developed for detecting the distance to an object such as a vehicle ahead of or approaching the present vehicle. Recently, a scanning radar apparatus for detecting not only the distance to the object, but also the direction of the object (observed from the present vehicle) has also been developed.
Such a scanning radar apparatus comprises a plurality of antennas, each antenna being arranged in a slightly different direction and thus radiating a beam in a slightly different direction and receiving a reflected beam from the relevant direction. The beams from these antennas are sent (and received) in turn, that is, not sent or received simultaneously, thereby determining the antenna which receives the reflected wave, that is, the direction of the generated reflected wave.
In the above scanning radar apparatus, each radio wave sending/receiving direction is called a channel, and the apparatus is called a multi-channel radar apparatus. This type of apparatus is an electronic scanning apparatus; however, the mechanical scanning by mechanically changing or deflecting the direction of a wave-sending/receiving antenna may also be used for detecting the direction of an object from which the reflected wave is generated and received.
As the directional resolution of the above-described type of scanning radar apparatus has improved, simultaneous multi-channel detection of an object (such as a vehicle ahead of the present vehicle) has become more common. In most of such radar apparatuses mounted in a vehicle and having high resolution, the reflected waves detected for each direction or each channel are divided into groups or clusters based on a predetermined characteristic, so that a target object from which the reflected waves are generated is presumed and detected. The following are examples for the characteristics used for the grouping: (i) the distance between the present vehicle and each reflection point (from which the relevant reflected wave was generated) is approximately the same over a plurality of adjacent channels, or (ii) the relative velocity of each reflection point with respect to the present vehicle is approximately the same.
When a vehicle or car having the above-explained scanning radar apparatus passes through a gate of an expressway or the like, the front ends of the left and right partitions walls (which limit the passage) are detected using the radar apparatus. In an example gate as shown in FIG. 6A, the left and right partitions P and Q which limit the left passage are respectively detected as reflection points p and q (see FIG. 6B) by using two adjacent channels. These two reflection points p and q are at approximately the same distance, and are also close to each other.
If a typical grouping is performed for these two reflection points p and q, then as shown by the dotted oval in FIG. 6B, it is judged that the reflection points are present on a continuum such as a large vehicle or a building (or structure). Such an incorrect judgment leads to the incorrect judgment that an obstacle is present in front of the present vehicle, so that an alarm may be raised for the driver, or an automatic control may be executed in the vehicle.
The above incorrect judgment can be prevented by interrupting the radar operation before the present vehicle passes through the gate, and restarting the radar operation after the vehicle has passed through the gate. However, to switch off and on the radar apparatus at a suitable timing imposes a great burden on the driver. In particular, if the vehicle passes through a non-stop type gate which will probably come into wide use, the above off/on switching must be performed very quickly. If such a quick switching cannot be performed, the vehicle may be automatically stopped, or a safety problem may occur due to failure to restart the radar after passing through the gate.
In consideration of the above circumstances, an objective of the present invention is to provide a gate which does not cause erroneous operation of a vehicle having a radar apparatus, without interrupting the radar apparatus when the vehicle passes the gate.
Therefore, the present invention provides a gate having a passage through which a radar-mounted vehicle passes, the vehicle having a radar apparatus which radiates electric, optical, or acoustic beams in a plurality of directions and receives reflected waves from an object so as to detect the object which generates the reflected waves, and the gate comprising two partition walls which limit the passage, the front ends of the partition walls being separately positioned along the direction of the passage. According to this structure, the front ends of the partition walls are not grouped by the radar apparatus even if a grouping operation is performed.
The present invention also provides a similar gate having the same basic structure, but the front end of only one of the partition walls has a structure for suppressing the frontward reflection of each incident radiated beam. Also in this structure, the front ends of the partition walls are not grouped by the radar apparatus even if a grouping operation is performed.
The present invention also provides a similar gate having the same basic structure, but the front ends of the partition walls have a structure for suppressing the frontward reflection of each incident radiated beam. According to this structure of the gate, the above front ends are not detected by the radar apparatus.
The following are preferable example methods for realizing the structure of the relevant front end for suppressing the frontward reflection of the beam:
(1) covering the front end with a material for absorbing the beam,
(2) inclining the front face of the front end in a manner such that the height of the relevant portion gradually decreases frontward, and
(3) forming a concavoconvex (i.e., regularly fluted or grooved) pattern on the front end so as to disperse the reflective directions of the incident beams.
As explained above, one or both of the partition walls detected by the radar apparatus are not grouped by the radar apparatus in a grouping operation, or both partition walls are not detected by the radar apparatus. Therefore, it is possible to effectively solve the problem relating to automatic control based on an incorrect judgment or determination of the radar apparatus.